8/7c WTF?

Maybe I'm mathematically challenged, but I can't make head or tail of the timezone information given in US TV schedules. The one we see the most involves times like 8/7c, pronounced "Eight, Seven Central", which I think means that a TV show is on at 8pm unless you're in the Central timezone, in which case it will be on at 7pm. This is definitely weird, because North America (let's exclude Alaska for now) has four timezones: Pacific (PST) = GMT-8 Mountain (MST) = GMT-7 Central (CST) = GMT-6 Eastern (EST) = GMT-5 ...and they all have their equivalent 'Daylight Savings Time' versions, one hour ahead of those with a 'D' in the acronym rather than an 'S'. So a timing of 8/7c would make sense to be advertised in the Eastern timezone, because 8pm Eastern is the same as 7pm Central. This would surely mean that a programme was being shown at the same physical time - which happened to be 8pm Eastern and 7pm Central. So why do we get these same times specified in California where we're on Pacific time? When they say 8/7c, do they mean that the whole country gets the TV show at 8pm local time unless you're in the Central timezone, in which case they show it at 7pm local time? This is just bizarre. It would be like the UK having TV times of 8/7(Rutland) where you'd see an episode of The Bill at 8pm unless you live in Thorpe By Water, in which case you'd see it at 7pm. This is probably a boon to people in the Alabama, though, because they get everything an hour before the rest of the country. Maybe they need the extra time to digest the content - perhaps it's a social service. And living in California, why do I care what time they'll be seeing the show in the Central timezone? Just to add confusion, there's also "E/P", which appears to mean "Eastern/Pacific", which I can only assume means it's shown at the same time (local time) throughout the country. Fox has examples of this in their 2006/2007 schedule, along with the more understandable "7:30pm ET/4:30pm PT" which clearly means that something is being shown at the same physical time across the whole country (live sports events, for instance). Be thankful if you live in a country with only one timezone (you know who you are).